1. Field of the Invention
The present invention relates to a display apparatus using liquid crystal display devices and, more particularly, to a display apparatus employing the liquid crystal devices and a projector having a scattering mode.
2. Related Background Art
A white light beam emitted from a light source 101 consisting of a halogen lamp, a metal halide lamp or the like, is reflected by a reflector 102 which assumes a rotational parabolic configuration having a focal point at the position of the light source 101. The parallel light beam passes through a filter 103 for blocking infrared rays and ultraviolet rays and thereafter is resolved into three color components--red, green and blue--by means of a color resolving optical system. The optical system consists of a dichroic mirror 104 which reflects the blue color but transmits the red and green colors, a dichromic mirror 105 which reflects the green color but transmits the red color and a total reflection mirror 106. The thus resolved luminous fluxes are incident on liquid crystal devices 107R, 107G or 107B corresponding to the respective color.
The liquid crystal devices 107R, 107G, 107B are each split into a plurality of pixels arranged in a matrix. The pixels are respectively independently driven by electric signals corresponding to the contents of a display and are scattered or become transparent with respect to incident light beams.
The light beams which have passed through the respective liquid crystal devices 107R, 107G, 107B become again the synthetic light beams as they pass through a color synthetic optical system consisting of a total reflection mirror 108, a dichroic mirror 109 which reflects the green color but transmits the blue color and a dichroic mirror 110 which reflects the red color but transmits the green and blue colors. Thereafter, the synthetic light beams pass through a Schlieren lens 111 and reaches a shield plate 112 having an aperture, the center of which is the optical axis. When passing through herein the pixels are kept in the transparent state in each pixel of the liquid crystal devices. In addition, outgoing light beams from the respective liquid crystal devices 107R, 107G, 107B travel through the aperture part of the shield plate 112 and are projected on an unillustrated screen by means of a projection lens 113. On the other hand, the outgoing light beams from the liquid crystal devices 107R, 107G, 107B after passing through the pixels kept in the scattered state are shielded by the shielding, art of the shield plate 112. The outgoing luminous fluxes do not reach the projection lens 113 and are not therefore projected on the unillustrated screen. An image can be displayed by selecting either the scattered condition or the transmitted condition.
FIG. 2 is a sectional view illustrating an example of the liquid crystal device employed for a projection in the conventional example shown in FIG. 1. A layer 203 is interposed between transparent glass substrates 201 and 201' disposed at a constant interval. Injected into the layer 203 are a macromolecule medium 203a and droplets 203b composed of positive dielectric anisotropic liquid crystal molecules diffused in the macromolecule medium 203a. Transparent electrodes 202, 202' are disposed adjacently on inner surfaces, confronting each other, of the glass substrates 201 and 201'. Materials of the macromolecule medium and the liquid crystal molecules are selected so that a refractive index of the macromolecule medium 203a is equal to a normal refractive index of the liquid crystal molecule. Exemplified is a method of forming the layer 203, the method involving the steps of: injecting a mixture of pre-polymerization monomer molecules and liquid crystal molecules between the glass substrates 201 and 201'; utilizing a property to cause a divergence from the liquid crystal when the monomer molecules are polymerized to become the macromolecules due to action of the heat or light; and thus forming the droplets composed of the liquid crystal molecules.
In the liquid crystal devices of FIG. 2, if no voltage is applied between the transparent electrodes 202 and 202', the liquid crystal molecules within the droplets 203b are oriented at random. Hence, the mean refractive index of the droplets 203b does not coincide with the refractive index of the macromolecule medium 203a, whereby the incident light on the liquid crystal molecules is scattered. Whereas if the voltage is applied, molecular major axes of the Liquid crystal molecules having the positive dielectric anisotropy are aligned in the perpendicular direction to the transparent electrode surfaces 202 and 202'. Therefore, the refractive indices thereof in the direction parallel to the layer consisting of the liquid crystal molecules and the macromolecule medium are coincident with each other. Hence, the incident light on the liquid crystal device, which has electric field vectors directed within the above-mentioned layer, travels straight without being scattered.
As a similar scattering type liquid crystal device, there may be exemplified one in which a low molecule liquid crystal is diffused at random in a network consisting of a macromolecule medium and one which uses a dynamic scattering mode (DS mode).
However, as indicated by a ray .alpha. in FIG. 1, among light beams scattered by some pixels, the ray having a large scattering angle incidents again on the other liquid crystal device 107G before being processed by the shield plate 112. Such a ray is partially re-scattered by the liquid crystal device undergoing the re-incidence and passes through the aperture part of the shield plate 112. The ray is projected as a ghost image or flare rays on the screen, resulting in a deterioration of the picture quality.
As described above, the apparatus where the plurality of liquid crystal devices shown in FIG. 1 has a problem in that the scattered light is insufficiently processed.
On the other hand, FIG. 3 is a sectional view illustrating the principal portion of a device for selecting either a scattered or non-scattered state in matix in the liquid crystal device shown in FIG. 2. The numeral 5 herein denotes a pixel electrode, and 6 represents a TFT element and a signal line. As depicted in the FIG., if incident light 10 is scattered by a liquid crystal layer 3, a part of the scattered rays enter adjacent pixels as indicated by arrows 12. This phenomenon is called an inter-pixel flare. A problem often arises in that the contrast of a projection image declines due to bleedings which have hitherto been produced by this flare.
In connection with the two problems described above, there exists a possibility in which the same situation may happen in all the display apparatuses using a mode for deflecting the light traveling direction (which hereinafter is defined as a "deflection mode") as in the case of an apparatus formed with a diffraction grating using the liquid crystal without being limited to the scattering mode liquid crystal.